Ovarian Masses and O-RADS

A Systematic Approach to Evaluating and Characterizing Adnexal Masses With Ultrasound

Ana Mitchell, MD; Austin Kwong, MD; Simran Sekhon, MD; John P McGahan, MD, FACR


Appl Radiol. 2021;50(3):24-31. 

In This Article

Ultrasound Imaging

In evaluating any pelvic mass, the first step is to determine if the mass is arising from the ovaries, the uterus, or another location. Once the anatomical origin is determined, imaging may be extremely helpful in establishing an accurate diagnosis. If the mass is of ovarian origin, for example, identifying its nature—cystic, solid, or complex—and ascertaining the presence of any fat or calcium in the mass will helps narrow the differential diagnoses.

Ultrasound is also invaluable for determining the cystic or solid nature of adnexal masses. Although a comprehensive discussion of all adnexal masses is beyond the scope of this pictorial review, Table 1 provides a list of some common cystic and solid adnexal masses that may be detected, and in most cases diagnosed, with sonography. In 2019, the Society of Radiologists in Ultrasound (SRU) updated its 2010 consensus statement on the management of asymptomatic ovarian and adnexal cysts.[2]

More recently, the ACR convened a consensus panel on risk stratification of ovarian-adnexal masses and management using an O-RADS™ classification system.[3] This system is more comprehensive than the SRU system in that it not only makes recommendations for classifying simple cysts, but also includes recommendations for risk stratifying more complex adnexal cysts. The O-RADS system also provides a lexicon of ultrasound descriptors to characterize, and ultimately classify, adnexal masses. For simple ovarian cysts in the premenopausal patient, the ACR recommends that 5–10 cm cysts be followed for 8–12 weeks to confirm their functional nature and to reassess for wall abnormalities. In postmenopausal females, simple cysts > 1 cm should be described but do not require follow-up imaging unless they are > 3 cm in size. The ACR O-RADS committee recommends a 1-year follow-up for 3–10 cm cysts in postmenopausal females. The complete review of this most recent SRU update and the O-RADS committee can be found in references 2 and 3.

While other guidelines in the literature are used for ultrasound evaluation of ovarian masses, the O-RADS system has been selected for review for multiple reasons. First, it provides an evidence-based standard lexicon for the use of terms that give a consistent diagnosis. Risk stratification is based upon the application of descriptors that are most predictive of malignancy from a large database, including pathology correlation with the International Ovarian Tumor Analysis (IOTA) group ultrasound rules for ovarian masses.

This system goes well beyond the SRU classification of simple cysts and considers other features of adnexal masses and corresponding management recommendations (Table 2). In addition, it is ultrasound-based, providing risk stratification and management based on imaging appearance of cysts. Descriptors of appearance include pure cysts, multilocular cysts, and multilocular cysts with solid components or solid masses. O-RADS considers diameter of the mass, presence of acoustic shadowing, unilocular versus multilocular cysts, cystic masses with papillary projection or solid component/solid mass appearance, and scoring of mass vascularity.[3] Color flow is graded as follows:

  1. – no flow;

  2. – minimal flow;

  3. – moderate flow; and

  4. – very strong flow.

A more detailed lexicon is available in source reference 3.

Risk stratification and management recommendations are based upon some of these parameters (Table 2). The O-RADS working group defined six categories of risk stratification: O-RADS 0, in which the adnexa are incompletely evaluated; O-RADS 1, the normal premenopausal ovary; O-RADS 2, almost certainly benign lesions with < 1% risk of malignancy; O-RADS 3, lesions with a low risk of malignancy (1–9%); O-RADS 4, lesions with an intermediate risk of malignancy (10-<50%); and O-RADS 5, high risk of malignancy (>50%).[3] O-RADS 2 lesions have fairly classic features such as hemorrhagic cysts (Figure 1), dermoid cysts (Figure 2), endometriomas (Figure 3), para-ovarian cysts, peritoneal inclusion cysts (Figure 4) and hydrosalpinx (Figure 5, Table 3). These lesions will be reviewed in detail here. For O-RADS 3 or greater lesions and sometimes in post-menopausal O-RADS 2 lesions, MRI may be valuable.

Figure 2.

Ovarian dermoid in separate patients. (A) A hyperechoic region (curved arrow) with distal shadowing and multiple hyperechoic lines and dots (arrow) are characteristic. (B) Mass with both hypoechoic and very densely echogenic regions (calipers), consistent with fat. (C) Typical hyperechoic lines and dots (arrow) within this mass and a hyperechoic region (curved arrow) with some acoustic shadowing (O-RADS 2).

Figure 3.

Endometrioma. (A) Initial ultrasound examination demonstrating adnexal mass (calipers) with homogeneous, ground-glass, low-level echoes. (B) Three-month follow-up ultrasound exam demonstrates similar findings with no color flow within the mass, confirming the diagnosis (O-RADS 2).

Figure 4.

Peritoneal inclusion cyst. (A) A cystic pelvic mass with septations, which may mimic a cystic ovarian neoplasm, but the ovary was separate (curved arrow). Fluid occupies the entire pelvis, following the contour of adjacent organs (U = uterus). (B) Coronal T2 MRI image demonstrates the right ovary with a cyst (O), extra-ovarian free fluid that does not have an oval appearance but acute angles (arrows) following the shape of adjacent organs (O-RADS 2).

Figure 5.

Hydrosalpinx. A parasagittal plane demonstrating a tubular structure (arrows) with incomplete septations posterior to the uterus (UT).